Exterior corners of drywall construction are presently constructed, most commonly, with an exterior metal corner bead having a pair of narrow flanges each diverging from a central semicircular small hollow bead, as shown in U.S. Pat. No. 2,851,741. The two flanges extend at an angle of about 90.degree. to one another, and are adhered or nailed in place over the wallboard edges. The flanges are then covered with a cementitious material, such as a joint compound, using the metal bead as a screed, and feathering out the opposite edge of the joint compound, to form a coat substantially coplanar with the wallboard surface, concealing the flanges, and terminating at the small raised bead at the corner.
To avoid a shrunken and cracked coating of the cementitious material, when it dries and hardens, it is generally necessary to apply the cementitious material in two or three coats, allowing prior coats to harden and dry before a subsequent coat is applied.